Conservation Non-Governmental Organisations (NGOs) are crucial actors in global conservation governance. They shape resource flows, establish cross-sector and cross-scale networks, and influence conservation discourses and practices. While research on conservation NGOs is growing, less attention has been paid to how conservation NGOs structure their networks. In this article, we interrogate the interpersonal social relationships that underpin the organisational dynamics of conservation NGOs engaged in transnational activities. Drawing on 45 semi-structured interviews with conservation professionals at NGOs based in Cambridge (UK), Bangkok (Thailand), and Vientiane (Lao PDR), we sketch two parallel and interacting dimensions: (a) the bureaucratic and institutional infrastructures that condition conservation flows and actor interactions; and (b) the interpersonal social relationships that pattern conservation flows between distant places and actors. We illustrate how such relationships are important for managing activities, responding to unexpected and unforeseen events, capitalising on funding opportunities by quickly mobilising an existing network, integrating new actors into project activities, enhancing cross-sector dialogues to mainstream biodiversity conservation, and accessing and influencing funders. Social relationships serve a crucial function due to the uncertain conditions in which conservation NGOs operate. Our results point to an important dimension of exclusion in transnational conservation networks.